<!DOCTYPE html>
<html lang="en">
<head>
    <meta charset="UTF-8">
    <meta name="viewport" content="width=device-width, initial-scale=1.0">
    <title>Document</title>
    <script src="./utils.js"></script>
</head>
<body>
    <button>移除</button>
    <div id="box">box</div>
    <script>
        var box = document.querySelector('#box')
        function foo () {
            console.log("box1")
        }
        on(box,'click',foo,true)
        on(document.querySelector('button'),'click',function(){
            off(box,'click',foo,true)
        })
    </script>
</body>
</html>